Control keyboard switch with cantilevered contact and diode matrix array

ABSTRACT

A low profile keyboard unit including an etched circuit board and a plurality of keyboard switches mounted on one surface thereof. Individual switches include housings configured to carry in self-contained fashion up to ten diodes plus a resistor, the leads from these elements being passed through holes in the board and flow soldered at the back side of the board.

United States Patent 1 1 Brady 1 1 May 1, 1973 154 CONTROL KEYBOARDSWITCH WITH 3,290,553 12 1966 Sapy ..317 101 CE CANTILEVERED CONTACT AND3,605,063 9/1971 Stewart ..317/101 CE x 3,290,439 12/1966 Willcox et a1..200/5 A X DIODE MATRIX ARRAY 3,240,885 3/1966 Grunfelder et a1...200/5 A [75] Inventor: John FQBrady, Clifton, NJ. 1,226,971 5/1917Hart ..200/166 SD UX 3,584,162 6/1971 KrakinowskL. ..200/S A [731Asslgflecgnjwersal Techmhgy Inc-1 Verona, 3,627,935 12 1971 Spievak..2o0 s A x [22] Filed; May 18 1971 Primary Examiner--J. R. ScottAn0rneyDean S. Edmonds et a1. [21] App]. No.: 144,606

' I [57] ABSTRACT U-S. Cl. A, A A low profile keyboard unit including anetched ir- [51] hit. Cl. ..H0lh 13/52 cuit board and a plurality fkeyboard Switches Fleld Search 5 6 R, mounted on one surface thereof.Individual switches 200/6 6 6 159 159 A, 166 include housings configuredto carry in self-contained 159 317/101 101 101 101 fashion up to tendiodes plus a resistor, the leads from CE these elements being passedthrough holes in the board and flow soldered at the back side of theboard. [56] References Cited I v 18 Claims, 5 Drawing Figures UNITEDSTATES PATENTS 3,551,616 12/1970 Juliusberger et al ..3l7/l0l CE XPatented May 1,1973 I 3,731,015

3 Sheets-Sheet 1 v INVENTOR JOHN F. BRADY Wm 9.9,1M

ATTORNEYS .Patentd May 1, 1973 3 Sheets-Sheet 2 INVENTOR JOHN F. BRADYATTORNEYS- CONTROL KEYBOARD SWITCH WITH CANTILEVERED CONTACT AND DIODEMATRIX ARRAY BACKGROUND OF INVENTION This invention relates generally toelectrical keyboards and more specifically relates to the multipleswitch type of keyboard commonly employed at computer terminals orsimilar environments whereat operator communication with an electronicsystem occurs.

Electric keyboards featuring an array of individual key switches havebeen in use for many years. Such keyboards have, for example, long beenutilized in electric typewriters, in which environment activation of theindividual keys effects striking of the type face-bearing elementsagainst the typewriter platen. In still more recent years, inconsequence of the enormous proliferation in data processing andcommunications systems, increased interest in keyboards and in theswitches utilized therewith has been evident. This has occurred byvirtue of the fact that communication with the cited systems is commonlyeffected through a manually operated keyboard. In particular an operatordesiring to enter information into the system or query the system withrespect to information already stored therein, will manually depressappropriate keys at the keyboard to enter data or initiate developmentof desired information.

In the electronic systems referred to a central problem has been that ofincorporating into the keyboard at commercially reasonable costs,sufficient flexibility to assure full control functions. While it is intheory always possible to associate sufficient logic circuitry with thekeyboard to assure, for example, that depressing of a selected key willprovide properly encoded signals to activate a desired function, suchresults are often achieved by complex and expensive means, and moreimportantly by means that add to the difficulty of assembling thekeyboard.

In accordance with the foregoing it may be regarded as an object of thepresent invention, to provide a keyboard for computer terminalinstallations or the like, which is of relatively low cost constructionand yet incorporates a wide range of control functions therein.

It is a further object of the invention, to provide an electricalcontrol keyboard capable of providing a wide range of encoded outputsfor interacting with a data processing or display system or the like,which keyboard is of such construction as to enable assembly thereof ina simple, inexpensive, and expeditious manner.

It is a further object of the present invention, to provide a keyboardfor computer terminal installations or the like, which incorporatesencoding functions in such a manner as to enable low profileconfigurations in the apparatus incorporating the keyboard.

SUMMARY OF INVENTION Now in accordance with the present invention, theforegoing objects, and others as will become apparent in the course ofthe ensuing specification, are achieved in a construction including anetched circuit board and a plurality of low profile keyboard switchesmounted against one surface thereof. The etched circuit board carries aplurality of generally parallel conductive tracks at the front and backsurfaces thereof, and at inthe cross sectional view of FIG. 1A, includesan insulatdividual switch positions plated holes are provided whichconnect to selected tracks. The switch housing is configured to carry incompletely self-contained fashion up to 10 diodes plus a resistor, thearrangement of these elements being such that direct connection to theholes of the underlying circuit board is readily made, therebyfacilitating assembly of a keyboard having complete encoding and controlfunctions associated therewith.

BRIEF DESCRIPTION OF DRAWINGS The invention is diagrammaticallyillustrated, by way of example, in the drawings appended thereto, inwhich:

FIG. 1 is an isometric, exploded view of a portion of a keyboard inaccordance with the invention;

FIG. 1A is a cross sectional view of the circuit board portion depictedin FIG. 1, taken along the line 1-1 therein;

FIG. 2 is an isometric, cutaway view of the switch portion of FIG. 1,showing elements of the switch in their assembled relationship; and

FIGS. 3 and 3A are respectively, partial front and rear plan views ofportions of the circuit board utilized with the present invention.

DESCRIPTION OF PREFERRED EMBODIMENT In FIG. 1 an isometric, explodedview appears, of a keyboard 2 in accordance with the present invention.The keyboard 2 is seen to include a switch 1 and an underlying circuitboard 4. The latter, as may be seen in ing board having a pattern 111 ofconductive lines on both sides thereof and a plurality of drilled holes112 which are provided with plated conductive surfacing 113. The mannerin which interconnection of switch 1 to pattern 111 is effected, andother specifics of the circuit board 4, will be further discussed hereinbelow in connection with the showings of FIGS. 3 and 3A.

The switch 1 itself is seen to include generally a housing 3, key top11, and plunger 9, all molded or otherwise formed of a nonconductiveplastic such as nylon or the like, and a pair of electrically conductiveelements in the form of a contact plate 5 and a contact leaf 7. Thehousing 3 is a generally box-shaped member, the interior of which isformed with a plate support platform 41 which is stepped outwardly atone end thereof to define a leaf support ledge 43. A channel 45 ispresent in platform 41 and is defined, as shown in FIG. 2, by acylindrical plunger support passage 47 which extends part of the waythrough housing 3 and then enlarges to a cylindrical bore 48. The latterflares out to an enlarged radius where it terminates at the back ofhousing 3, thereby defining a shoulder 50. A pair of ears 40, 42 areformed as partial arcs about channel 45. An adjoining channel 49 isformed in leaf support ledge 43 and is seen to be in communication withthe forward part of passage 47. Bore 48 at the rear of housing 3 isclosed by a spring plate 22, which is formed of plastic or the like andis received at shoulder 50.

Housing 3 is provided with a plurality of cylindrical passages 33 andwith a single transversely elongated passage 53, all of which extendcompletelythrough the housing to open at the back end thereof. Thepassages 33 with the exception of the passage identified as 33a are usedto carry diodes 35 therein. It is evident that when such diodes arenested in passages 33, the leads 35a and 35b thereof are accessible forconnection at both ends of passage 33. The excepted passage, 33a, isutilized for nesting the metal contact pin 19 which via its lead 19apermits external common connection to contact plate 5. The elongatedpassage 53 is also seen to be adapted for receipt therein inside-by-side fashion of both a diode and a resistor. In a representativeapplication of the present switch, up to diodes and 1 resistor mayactually be present in housing 3, with connection to underlying circuitboard 4 being directly effected at the exposed leads of the electricalcomponents such as at 35b. This large number of selfcontained diodesmeans in practice that the switch 1 can typically be used to provide avery full range of control and encoding in the keyboard in which it isincorporated. Typically, for example, sufficient switched connectionsare available to provide encoding for up to 7 bit numbers (including anadditional bit for parity), plus additional switched connections forroll-over, shift inhibit, and control inhibit functions.

The metallic contact plate 5 is seen in FIG. 1 to be adapted to restupon platform 41 with the two protruding bosses 55 and 57 passingthrough aligned holes 59 and 61 in the plate. A series of circular holes39 and an elongate slot 63 are present in plate 5, these elements beingupon assembly registrable with the various underlying passages inhousing 3. In similar fashion the rectangular opening 65 registers withchannel 45 in the housing. A tab 67 at the bottom of plate 5 assists inpositioning the plate during assembly and closes the forward part ofchannel 49.

Contact leaf 7, as is seen in FIG. 1, is a metallic, leaflike structure,typically formed of a thin gauge spring steel. It is a single, unitstamped structure, including a base portion 69 which is bifurcated intothe branches 23 and 25, the branches in turn being trifurcated at theiradjacent but noncontacting end portions into sets of three contactfingers 23a, 23b, 23c and 25a, 25b, 25c. Each individual contact fingeris seen to be relatively independently displaceable transverse to thegeneral plane of leaf 7. It will also be seen that each of the fingers23a, 25a, etc., are bent downwardly at their midpoints 70 so that theends thereof are normally displaced somewhat in the direction of plate5.

It is seen that when the various elements are assembled in switch 1, thebase portion 69 of leaf 7 rests upon ledge 43 with the bosses 71 and 73of the ledge protruding through circular holes 75 and 77 in the leaf. Anadditional circular hole 79 in the leaf permits passage of the contactpin 21 (the head thereof being held at the leaf) through an alignedpassage 81 in housing 3. It will be clear that when plate 5 and leaf 7are mounted in housing 3 the leaf 7 is only supported at its base 69,with branches 23 and 25 being cantilevered over the spaced plate 5.

Contact between the contact leaf 7 and plate 5 is effected by anoperators depressing key top 11. The interior of the key top 11 isformed with a cavity (not explicitly shown) adapted to receive endportion 91 of plunger 9 therein.

The plunger 9 may conveniently be molded (of plastic or the like) as asingle unit. It includes, in addition to end portion 91 and cross rib92, a pad portion 93, and a foot portion 95. The latter, which isapproximately cylindrical in shape, is adapted to pass through theopenings 97 and 65 of contact leaf 7 and contact plate 5, and intochannel 47 of housing 3. Portion 95 includes a longitudinal slot 99extending along one side thereof. Slot 99 cooperates with a key way 100extending into housing 3 from the edge of car 42 to the back of passage47, so as to assure that even when plunger 9 is at its most withdrawnposition, very little wobble is evidenced at key top 11. Foot portion 95terminates in a tip 102 which is heat flattened after passage throughretaining washer 106 to prevent withdrawal of plunger 9 from the housingA return spring 17 bears against spring plate 22; spring 17, as key top11 is depressed, is compressed, and provides a restoring force viawasher 106 for returning the key top to its original position.

By examing FIG. 1 in conjunction with the cutaway isometric view of FIG.2, it may be seen that plunger 9 is provided on side 101 of foot portion95, with a depressed flattened portion 29 adapted to receive a portionof the tactile ball 13 therein. The showing of FIG. 2 depicts the switch1 of FIG. 1 rotated 90 in a counterclockwise direction. Tactile ball 13is a small plastic or metallic ball of radius larger than the height ofthe shoulder 104 defined (FIG. 3) between portion 29 and the unflattenedportion of foot 9. Ball 13 is biased into contact with face 101 by thetactile spring 15 nested in cavity 103 of housing 3. The cutaway view ofFIG. 2 depicts the switch 1 in its normal, undepressed condition. Thusit is seen that under these circumstances tactile ball 13 is firmlyseated upon flat 29 and against shoulder 104, and in combination withthe restoring force provided by spring 17, offers considerableresistance to downward movement of plunger 9, in that such movementcannot occur until ball 13 is displaced away from the stop provided byshoulder 104. Upon the operators continuing to increase his fingerpressure upon key 11, however, a threshold level is reached upon whichball 13 suddenly moves outwardly from flat 29 and over shoulder 104, inconsequency of which a sudden precipitous drop in resistance to movementof the key occurs.

The sequence of events described, has several very importantconsequences in the present invention. Firstly, it will be evident thata most excellent tactile feedback is present for the keyboard operator,in that the latter may most readily sense the sudden disengagement oftactile ball 13 and has a clear indication of key depression. Secondly,the comparatively high threshold force required to displace ball 13eliminates the phenomenom of teasing" whereby an operator may play witha key and accidentally activate it. Thirdly, once sufficient force isapplied to displace the ball 13, the resistance drops so suddenly thatmuch excess force is then present, assuring a complete driving home ofplunger 9 to provide a clear hit" on the switch.

Actual electrical contact in switch 1 is then brought about by pad93'bearing against fingers 23a, 23b, 23c, and 25a, 25b, 250. Such actionis evident both from the exploded view of FIG. 1 and the cutaway view ofFIG. 2. It will also be evident from these views that as the pad 93advances, flexure occurs in both the branches 23,25, and in the fingers23a, 23b, 23c, and 25a, 25b, 25c, in turn advancing these elementstoward plate 5. It

will also be clear that the tips of the six fingers will make initialcontact with plate 5, but that as plunger 9 advances further, flexure ofbranches and fingers will laterally displace the points of contact in acontinuing wiping action.

It is important to appreciate that the six fingers, 23a, 250, etc.provide six separate contact points for the closing of the switch. Notonly is the conta t resistance in such an arrangement quite low, butmoreover the reliability of operation is much enhanced by the largelyindependent movement and contact made by the individual fingers. Inaddition, as has been previously pointed out, the ensuing contactbetween fingers and plate 5 is a wiping contact produced by a continuingimpulse, in consequence of which exceedingly little bounce can occur asthe switch circuit is closed.

As has previously been indicated a principal advantage of the presentinvention derives from the simplistic manner in which assembly may beeffected for a keyboard unit yet retaining full control capabilities.This aspect of the invention may be best understood by I consideringinconjunction with FIG. 1, the plan views of FIGS. 3 and 3A. These latterviews depict on an enlarged scale, portions 115 and 117 of circuit board4, taken from respectively opposite sides of board 4. Portions 115 and117 are actually back-to-back elements of board 4, which is to say thatthe points designated X and Y in FIG. 3, will on the actual circuitboard overlie the points designated X and Y in FIG. 3A.

The portions 1 l5 and l 17 of circuit board 4 shown in FIGS. 3 and 3A,represent, it will be appreciated, only a fraction of the entire circuitboard present in a full kevboard. Thus, in this connection, a dottedoutline 119 appears in FIG. 3, representing the approximate mountedperimeter of a switch such as switch 1 in FIG. 1; and a dotted outline119A appears in FIG. 3A representing the relation of the approximatemounted perimeter of the same switch to portion 117 of circuit board 4.It will be readily apparent that the mounting positions for but foursuch switches are set forth in FIGS. 3 and 3A. In a typical keyboard atotal of 61 such positions may actually be present, four parallel rowsof mounting positions being utilized to accommodate this totality.Portions of but two such rows, 120 and 121 are shown in FIGS. 3 and 3A,in that the connection scheme and mode of operation of theinvention isfully evident from the limited depiction.

The conductive patterns 111 on circuit board 4 are established byconventional photoetching techniques. In particular, beginning with aninsulating board 110 clad on each face with a copper layer, aphotoresist is applied and appropriate exposure to actinic radiationeffected so as upon etching to leave the desired conductive pattern.Drilled holes are then formed, as at 122, which holes are then plated asat 113 in 'FIG. 1A so that leads inserted therethrough may be connectedto portions of pattern 111 which in turn are connected to selectedholes.

It will be specifically appreciated that each mounting row 120, 121,etc. is defined on portion 115 of board 4 by a series of generallyparallel conductive tracks 123, a further series of parallel conductivetracks 125 being present on the underlying portion 117 of the board. Itwill be seen that eight such tracks 123 are present in each such row;five such tracks are within the perimeter 119 and an additional sixtracks underlie the perimeter 119 on the opposite side (FIG. 3A) ofboard 4 so that a total of l 1 rows are actually accessible for directconnection to the pins such as 35b projecting from diode and resistorelements positioned in housing 3 of switch 1 and contact pins such aspin 21.

The scheme of connection for the various diode and resistor elementsshould now be clear. In particular, examination of portions and 117 inFIGS. 3 and 3A will establish that each conductively plated hole at amounting position is electrically connected to at least one of theparallel tracks 123, 125, and that each such track in turn connects toone of a plurality of conductive lines 127 at the border of board 4.Thus, for example, a hole 129 is connected to the conductive line 130via the track 131 on board portion 115, and thence through plated hole133 and track 132 on portion 117 to plated hole 134. Conductive lines127, in turn, include terminal points 135 whereat connections may beeffected for other components of the computer terminal incorporating thepresent keyboard.

In a typical application line 136 may serve as a ground and line 137 asa source of V+ voltage. These two lines are seen to be connectedrespectively to pins 138 and 139. Depending on the particular groupingof diodes in a given switch 1, it will thus be clear that since theleads 35a (FIG. 1) of the several diodes are connected to contact plate5, closing of the switch contacts will cause signals to appear at suchof terminals 135 as are electrically adjoined to the circuit throughdiode (or resistor) contacts with tracks 123 and 125. Dependingtherefore on the number and arrangement of diodes, differing groupingsof signals appear at the terminals 135, and the signal groupings interms of presence or absence of an output at the several terminals maybe associated with a given letter, symbol, or so forth. That is to saythat with the representative eleven lines 127, up to 11 bits ofinformation can be presented upon depressing of a single key in thekeyboard 2, and the bit sequence may be associated by any standardencoding technique with given symbols, graphics, or so forth.

It will be appreciated that all that is necessary to achieve initialinstallation or replacement of a given switch 1, is to place such switchwith its properly protruding leads (such as lead 35b in FIG. 1) upon itsappropriate position on the keyboard. The leads then pass through theseveral conductively plated holes of the keyboard, and the switch isthen rendered fast to the keyboard by simply soldering the leads toadjacent points at the holes. Where a large group of switches isattached at a single time, such soldering may be effected in a singleoperation, by standard methods such as by dip soldering.

While the present invention has been particularly described in terms ofa specific embodiment thereof, it will be evident in view of the presentdisclosure, that numerous variations upon the invention are now enabledto those skilled in the art, which variations are properly within thetrue scope of the present teaching. Accordingly, the invention is to bebroadly construed, and limited only by the scope and spirit of theclaims now appended hereto.

I claim:

1. A keyboard unit comprising in combination:

a circuit board including a plurality of generally parallel conductivetracks at least one of which is connectable to a source of inputpotential, a plurality of conductively plated holes formed through saidboard and connected to said tracks, and a series of output terminalsconnected to said tracks; plurality of keyboard switches mounted on saidboard over said holes, each of said switches including an individualhousing, a fixed conductive plate therein, a movable contact, actuatingmeans for moving said movable contact into engagement with said fixedconductive plate, and space for carrying similarly shaped switchingdiodes; and

plurality of diodes, at least one diode being mounted in each keyboardswitch, each diode having a pair of leads one of which protrudes fromsaid housing, passes directly through a hole in the circuit board and isjoined to the hole boundary to form an electrical connection to one ofsaid conductive tracks and the other of which is connected to the fixedconductive plate of the keyboard switch in which it is mounted, wherebysignals may be established at the output terminals upon operation of theactuating means in accordance with the arrangement and number of diodesin said keyboard switch.

2. Apparatus in accordance with claim 1 wherein said conductive tracksand the overlying switches are arranged in a plurality of parallel rows.

3. Apparatus in accordance with claim 1, wherein said conductive tracksare present on both sides of said board, and at least some of the trackson opposite sides of said board are electrically connected to oneanother through said conductively surfaced holes.

4. Apparatus in accordance with claim 3 wherein at least of said tracksunderlie each switch, whereby direct connection to at least an equalnumber of said switching diodes is enabled.

5. Apparatus in accordance with claim 4 wherein each diode in a keyboardswitch is connected to a different underlying track.

6. Apparatus in accordance with claim 1 wherein:

the movable contact is supported in cantilevered fashion in its housing,said movable contact being positioned approximately in parallel spacedrelationship to said fixed conductive plate; and

the actuating means comprises plunger means movable into said housing ina direction transverse to the plane of said movable contact, saidplunger means being adapted upon said movement to bear upon said movablecontact and displace the cantilevered portion thereof into contact withsaid fixed conductive plate to close the keyboard switch.

7. Apparatus in accordance with claim 6 wherein said movable contactcomprises a generally flattened member having a base portion and a pairof branch portions extending from said base portion and in turnbranching into multiple contact fingers, said movable contact beingsupported in said housing at said base portion, said branch portionsbeing cantilevered over said fixed conductive plate.

8. Apparatus in accordance with claim 7 wherein the base portion, thebranch portions and contact fingers surround and define an opening insaid movable contact.

9. Apparatus in accordance with claim 8 wherein said plunger means bearson said contact fingers to displace them into contact with said fixedconductive plate.

10. Apparatus in accordance with claim 2 wherein the base portion, thebranch portions and the finger portions of said movable contact surroundand define an opening in said contact, an opening being present in saidfixed conductive plate, and a plunger support passage being present insaid housing, and wherein said plunger includes a foot portion adaptedto pass through said openings and into said passage of'said housing anda laterally extending pad portion which presses against said fingers ofsaid movable contact to effect said displacement thereof as said padcontacts said movable contact.

'11. Apparatus in accordance with claim 10, wherein said foot is ofgenerally cylindrical shape, said depressed portion thereon comprising aflat on said cylinder, the said tactile ball resting against theshoulder defined between said flat and the remaining portion of saidcylinder when said plunger is in an undepressed condition. l2. Apparatusin accordance with claim 10, wherein said plunger support passageincludes a keyway extending longitudinally therein and said plunger foot.includes a longitudinal slot for engaging said keyway and steadying Ithe lateral movement of said plunger, whereby to reduce wobble at saidkey top.

13. Apparatus-in accordance with claim 6, further including a key topinterconnected with said plunger means to effect said displacementthereof upon operator pressure. i a

14. Apparatus in accordance with claim 7, further including a returnspringcompressible by said displacement of said plunger means to providea restoring force for returning said plunger to its original position.

15. Apparatus in accordance with claim 6, wherein said housing is formedwith a transverse platform for supporting said contact plate, saidplatform being stepped upwardly at an end thereof to define a narrowsupport ledge for the base portion of said contact leaf.

16, Apparatus in accordance with claim 6 wherein the source of inputpotential is connected to the movable contact.

17. Apparatus in accordance with claim 6 wherein:

said movable contact comprises a member having a base portion, a branchportion extending from said base portion, and multiple contact fingersconnected to said branch portion and cantilevered over said fixedconductive plate; and said plunger means bears on said contact fingersto displace them into contact with said fixed conduc tive plate.

18. Apparatus in accordance with claim 6, wherein said plunger meanscarries a depressed portion-on a face thereof parallel to the directionof said displacement, and wherein said switch further includes a tactileball and a tactile spring nested in said housing for biasing said ballagainst said plunger face, said spring and ball being nested at aposition such that when the plunger is in an undepressed position thetactile ball rests in said depressed portion and thereby provides aresistive force to displacement of said plunger, sufficient force uponsaid plunger acting to move said plunger and displace said balloutwardly from said depressed portion whereby to suddenly reduce thesaid resistive force and provide tactile indication to the operator ofmovement of said plunger.

1. A keyboard unit comprising in combination: a circuit board includinga plurality of generally parallel conductive tracks at least one ofwhich is connectable to a source of input potential, a plurality ofconductively plated holes formed through said board and connected tosaid tracks, and a series of output terminals connected to said tracks;a plurality of keyboard switches mounted on said board over said holes,each of said switches including an individual housing, a fixedconductive plate therein, a movable contact, actuating means for movingsaid movable contact into engagement with said fixed conductive plate,and space for carrying similarly shaped switching diodes; and aplurality of diodes, at least one diode being mounted in each keyboardswitch, each diode having a pair of leads one of which protrudes fromsaid housing, passes directly through a hole in the circuit board and isjoined to the hole boundary to form an electrical connection to one ofsaid conductive tracks and the other of which is connected to the fixedconductive plate of the keyboard switch in which it is mounted, wherebysignals may be established at the output terminals upon operation of theactuating means in accordance with the arrangement and number of diodesin said keyboard switch.
 2. Apparatus in accordance with claim 1 whereinsaid conductive tracks and the overlying switches are arranged in aplurality of parallel rows.
 3. Apparatus in accordance with claim 1,wherein said conductive tracks are present on both sides of said board,and at least some of the tracks on opposite sides of said board areelectrically connected to one another through said conductively surfacedholes.
 4. Apparatus in accordance with claim 3 wherein at least 10 ofsaid tracks underlie each switch, whereby direct connection to at leastan equal number of said switching diodes is enabled.
 5. Apparatus inaccordance with claim 4 wherein each diode in a keyboard switch isconnected to a different underlying track.
 6. Apparatus in accordancewith claim 1 wherein: the movable contact is supported in cantileveredfashion in its housing, said movable contact being positionedapproximately in parallel spaced relationship to said fixed conductiveplate; and the actuating means comprises plunger means movable into saidhousing in a direction transverse to the plane of said movable contact,said plunger meanS being adapted upon said movement to bear upon saidmovable contact and displace the cantilevered portion thereof intocontact with said fixed conductive plate to close the keyboard switch.7. Apparatus in accordance with claim 6 wherein said movable contactcomprises a generally flattened member having a base portion and a pairof branch portions extending from said base portion and in turnbranching into multiple contact fingers, said movable contact beingsupported in said housing at said base portion, said branch portionsbeing cantilevered over said fixed conductive plate.
 8. Apparatus inaccordance with claim 7 wherein the base portion, the branch portionsand contact fingers surround and define an opening in said movablecontact.
 9. Apparatus in accordance with claim 8 wherein said plungermeans bears on said contact fingers to displace them into contact withsaid fixed conductive plate.
 10. Apparatus in accordance with claim 2wherein the base portion, the branch portions and the finger portions ofsaid movable contact surround and define an opening in said contact, anopening being present in said fixed conductive plate, and a plungersupport passage being present in said housing, and wherein said plungerincludes a foot portion adapted to pass through said openings and intosaid passage of said housing and a laterally extending pad portion whichpresses against said fingers of said movable contact to effect saiddisplacement thereof as said pad contacts said movable contact. 11.Apparatus in accordance with claim 10, wherein said foot is of generallycylindrical shape, said depressed portion thereon comprising a flat onsaid cylinder, the said tactile ball resting against the shoulderdefined between said flat and the remaining portion of said cylinderwhen said plunger is in an undepressed condition.
 12. Apparatus inaccordance with claim 10, wherein said plunger support passage includesa keyway extending longitudinally therein and said plunger foot includesa longitudinal slot for engaging said keyway and steadying the lateralmovement of said plunger, whereby to reduce wobble at said key top. 13.Apparatus in accordance with claim 6, further including a key topinterconnected with said plunger means to effect said displacementthereof upon operator pressure.
 14. Apparatus in accordance with claim7, further including a return spring compressible by said displacementof said plunger means to provide a restoring force for returning saidplunger to its original position.
 15. Apparatus in accordance with claim6, wherein said housing is formed with a transverse platform forsupporting said contact plate, said platform being stepped upwardly atan end thereof to define a narrow support ledge for the base portion ofsaid contact leaf.
 16. Apparatus in accordance with claim 6 wherein thesource of input potential is connected to the movable contact. 17.Apparatus in accordance with claim 6 wherein: said movable contactcomprises a member having a base portion, a branch portion extendingfrom said base portion, and multiple contact fingers connected to saidbranch portion and cantilevered over said fixed conductive plate; andsaid plunger means bears on said contact fingers to displace them intocontact with said fixed conductive plate.
 18. Apparatus in accordancewith claim 6, wherein said plunger means carries a depressed portion ona face thereof parallel to the direction of said displacement, andwherein said switch further includes a tactile ball and a tactile springnested in said housing for biasing said ball against said plunger face,said spring and ball being nested at a position such that when theplunger is in an undepressed position the tactile ball rests in saiddepressed portion and thereby provides a resistive force to displacementof said plunger, sufficient force upon said plunger acting to move saidplunger and displace said ball outwardly from said depressed portionwhereby to suddenly reduce the said resistivE force and provide tactileindication to the operator of movement of said plunger.